Byzantine state machine replication for the masses

Tese de doutoramento, Informática (Ciência da Computação), Universidade de Lisboa, Faculdade de Ciências, 2018The state machine replication technique is a popular approach for building Byzantine fault-tolerant services. However, despite the widespread adoption of this paradigm for crash fault-tolerant systems, there are still few examples of this paradigm for real Byzantine fault-tolerant systems. Our view of this situation is that there is a lack of robust implementations of Byzantine fault-tolerant state machine replication middleware, and that the performance penalty is too high, specially for geo-replication. These hindrances are tightly coupled to the distributed protocols used for enforcing such resilience. This thesis has the objective of finding methodologies for enhancing robustness and performance of state machine replication systems. The first contribution is Mod-SMaRt, a modular protocol that preserves optimal latency in terms of the communications steps exchanged among processes. By being a modular protocol, it becomes simpler to validate and implement, thus resulting in greater robustness; by also preserving optimal message-exchanges among processes, the protocol is capable of delivering desirable performance. The second contribution is concerned with implementing Mod-SMaRt into BFTSMART, a reliable and high-performance codebase that was maintained and improved over the entire course of the PhD that offers multicore-awareness, reconfiguration support, and a flexible API. The third contribution presents WHEAT, a protocol derived from Mod-SMaRt that uses optimizations shown to be effective in reducing latency via a practical evaluation conducted in a geo distributed environment. We additionally conducted an evaluation of both BFT-SMART and WHEAT applied to a relational database middleware and an ordering service for a permissioned blockchain platform. These evaluations revealed encouraging results for both systems and validated our work conducted in the geo-distributed context.A técnica de replicação máquina de estados é um paradigma popular usado em vários sistemas distribuídos modernos. No entanto, apesar da adoção deste paradigma em sistemas reais tolerantes a faltas por paragem, ainda existem poucos exemplos de sistemas reais tolerantes a faltas bizantinas. Segundo a nossa experiência nesta área de investigação, isto deve-se ao fato de existirem poucas concretizações robustas para replicação máquina de estados tolerante a faltas bizantinas, assim como uma perda de desempenho demasiado elevada, especialmente em ambientes geo-replicados. A razão fundamental para a existência destes obstáculos vem dos protocolos distribuídos necessários para assegurar este tipo de resiliência. Esta tese tem como objetivo explorar metodologias para a robustez e eficiência da replicação máquina de estados. A primeira contribuição da tese é o algoritmo Mod-SMaRt, um protocolo modular que preserva latência ótima em termos de passos de comunicação executados pelos processos. Sendo um protocolo modular, torna-se mais simples de validar e concretizar, o que resulta em maior robustez; ao preservar troca de mensagens ótima entre processos, também é capaz de entregar um desempenho desejável. A segunda contribuição consiste em concretizar o protocolo Mod SMaRt na ferramenta BFT-SMART, uma biblioteca fiável de alto desempenho, mantida e melhorada ao longo de todo o período correspondente ao doutoramento, capaz de suportar arquiteturas multi-núcleo, reconfiguração do grupo de réplicas, e uma API de programação flexível. A terceira contribuição consiste em um protocolo derivado do Mod-SMaRt designado WHEAT, que usa otimizações que demostraram serem eficientes na redução da latência segundo uma avaliação prática em ambiente geo-replicado. Adicionalmente, foram também realizadas avaliações de ambos os protocolos quando aplicados num middleware para base de dados relacionais, e num serviço de ordenação para uma plataforma blockchain. Ambas as avaliações revelam resultados encorajadores para ambos os sistemas e validam o trabalho realizado em contexto geo-distribuído.Projeto IRCoC (PTDC/EEI-SCR/6970/2014); Comissão Europeia, FP7 (Seventh Framework Programme for Research and Technological Development), projetos FP7/2007-2013, ICT-25724

On Learning

This is a philosophical work that develops a general theory of ontological objects and object-relations. It does this by examining concepts as acquired dispositions, and then focuses on perhaps the most important of these: the concept of learning. This concept is important because everything that we know and do in the world is predicated on a prior act of learning. A concept can have many meanings and can be used in a number of different ways, and this creates difficulty when considering the nature of objects and the relationships between them. To enable this, David Scott answers a series of questions about concepts in general and the concept of learning in particular. Some of these questions are: What is learning? What different meanings can be given to the notion of learning? How does the concept of learning relate to other concepts, such as innatism, development and progression? The book offers a counter-argument to empiricist conceptions of learning, to the propagation of simple messages about learning, knowledge, curriculum and assessment, and to the denial that values are central to understanding how we live. It argues that values permeate everything: our descriptions of the world, the attempts we make at creating better futures and our relations with other people

The Israeli response to Jewish extremism and violence

This book looks at the theoretical issue of how a democracy can defend itself from those wishing to subvert or destroy it without being required to take measures that would impinge upon the basic principles of the democratic idea, such as human rights, freedom of speech and the freedom to form political organisations. This dilemma has captured the attention of philosophers as well as legal scholars for many years, but has thus far been rarely studied employing institutional and social frameworks. In this book such frameworks are incorporated into the discussion of the 'paradox' in an attempt to provide an answer to the question: is there a golden path which can reconcile between the democratic polity's need to defend itself and, at the same time, maintain responsibility to protect and safeguard the basic right of its citizens? It takes as its case study of this issue the Israeli response to Jewish extremism and violence, which tests the theoretical framework outlined in the first chapter of the book. Providing an extensive diachronic scrutiny of the State's response to extremist political parties, violent organisations and the infrastructure of extremism and intolerance within Israeli society. It emphasises the dynamics of the response and the factors which encourage or discourage the shift from less democratic and more democratic models of response. The book is unique in that it links social and institutional perspectives to the study. The book will be vital reading for students of peace studies, conflict analysis, international relations and international politics, as well as students of the political situation in the Middle east

Psychotropes: Models of Authorship, Psychopathology, and Molecular Politics in Aldous Huxley and Philip K. Dick

Among the so-called “anti-psychiatrists” of the 1960s and ‘70s, it was Félix Guattari who first identified that psychiatry had undergone a “molecular revolution.” It was in fact in a book titled Molecular Revolutions, published in 1984, that Guattari proposed that psychotherapy had become, in the de¬cades following the Second World War, far less personal and increasingly alienating. The newly “molecular” practices of psychiatry, Guattari mourned, had served only to fundamentally distance both patients and practitioners from their own minds; they had largely restricted our access, he suggested, to human subjectivity and consciousness. This thesis resumes Guattari’s work on the “molecular” model of the subject. Extending on Guattari’s various “schizoanalytic metamodels” of hu¬man consciousness and ontology, it rigorously meditates on a simple ques¬tion: Should we now accept the likely finding that there is no neat, singular, reductive, utilitarian, or unifying “model” for thinking about the human subject, and more specifically the human “author”? Part 1 of this thesis carefully examines a range of psychoanalytic, psychi¬atric, philosophical, and biomedical models of the human. It studies and re¬formulates each of them in turn and, all the while, returns to a fundamental position: that no single model, nor combination of them, will suffice. What part 1 seeks to demonstrate, then, is that envisioning these models as differ¬ent attempts to “know” the human is fruitless—a futile game. Instead, these models should be understood in much the same way as literary critics treat literary commonplaces or topoi; they are akin, I argue, to what Deleuze and Guattari called “images of thought.” In my terminology, they are “psycho¬tropes”: images with their own particular symbolic and mythical functions. Having thus developed a range of theoretical footholds in part 1, part 2 of the thesis—beginning in chapter 4—will put into practice the work of this first part. It will do so by examining various representations of authorship by two authors in particular: Aldous Huxley and Philip K. Dick. This part will thus demonstrate how these author figures function as “psychoactive scriv¬eners”: they are fictionalising philosophers who both produce and quarrel with an array of paradigmatic psychotropes, disputing those of others and inventing their own to substitute for them. More than this, however, the second part offers a range of detailed and original readings of these authors’s psychobiographies; it argues that even individual authors such as Huxley and Dick can be seen as “psychotropic.” It offers, that is, a series of broad-ranging and speculative explanations for the ideas and themes that appear in their works—explanations rooted in the theoretical work of the first part. Finally, this thesis concludes by reaffirming the importance of these authors’s narcoliteratures—both for present-day and future literary studies, and beyond. For while Huxley and Dick allow us to countenance afresh the range of failures in the history and philosophy of science, they also prom¬ise to instruct us—and instruct science—about the ways in which we might move beyond our received mimetic models of the human

Intellectual formations in the Romantic period: a comparative study of cultural politics and social criticism in the British public sphere, 1802-32

This thesis examines rival intellectual practices in the early nineteenth century through the theoretical framework of the Habermasian public sphere. Comparing the work of post-Scottish Enlightenment critics such as Francis Jeffrey, Henry Brougham and Thomas Carlyle, and their English radical plebeian counterparts, William Cobbett, T.J. Wooler and Thomas Spence, the thesis examines the bases of two divergent strategies of cultural resistance to the social crises of industrialism. By highlighting the ways in which a central literary genre like periodical social criticism was materially constructed out of distinctive modes of intellectual sociability, we can rethink the comparative political efficacy of rival idealist and materialist forms of intellectual praxis during a crucial transitional period. The argument serves as a corrective to the canonical studies of the 'big six' of English Romanticism by foregrounding cultural narratives occluded in traditional Romanticist scholarship: the underappreciated contribution made to Romantic period cultural history by marginalized national traditions, generic forms, and intellectual practices. Reflecting the ideological complexity of these competing critical discourses and cultural narratives, and recognizing the value of a multi-perspectival approach, the dissertation is divided into two sections. The first offers a theoretical and historical overview of the British public sphere, while the second engages through a series of discrete readings with the texts of the critics themselves